Laser-based optical switches and logic

ABSTRACT

Optical switches and logic devices comprising microstructure-doped nanocavity lasers are described. These switches and logic devices have gain and thus can be cascaded and integrated in a network or system such as for example on a chip. Exemplary switching elements switch the intensity, wavelength, or direction of the output. Exemplary logic devices include AND, OR, NAND, NOR, NOT, and XOR gates as well as flip-flops. Microfluidic sorting and delivery as well as optical tweezing and trapping may be employed to select and position a light emitter in a nanooptical cavity to form the nanolaser.

PRIORITY APPLICATION

This application claims the benefit of U.S. Provisional Application No.60/511,753, entitled “Optical Logic With Gain: Photonic CrystalNanocavity Switches,” filed Oct. 15, 2003, the entire disclosure ofwhich is hereby incorporated by reference herein and made a part of thisspecification.

The U.S. Government has certain rights in this invention pursuant toGrant No. F49620-02-1-0418 awarded by The Air Force Office of ScientificResearch.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present teachings relate to optical switches and optical logichaving gain and methods of implementing switching and logic with laserstructures.

2. Description of the Related Art

Light offers many advantages when used to propagate information, theforemost of which are increased speed and bandwidth. In comparison withelectrical signals, signals transmitted optically can be modulatedfaster and can include an even greater number of separate channelsmultiplexed together. The signal may correspond to voice or data whichis to be transmitted over a distance between, e.g., two phones acrossthe country or the world, two computers in a network, or two componentsin a computer.

To increase data throughput, numerous optical signals at differentwavelengths can be multiplexed and transmitted together along a singleoptical path. This optical path can be selectively switched and variedto direct the different optical signals such as different channels tothe appropriate destination. Accordingly, fast optical switches forswitching are desirable.

If available, optical logic components for processing and manipulatingoptical signals could be used to implement more sophisticated logicaloperations optically. In addition to a voice or data communicationsystem, such logic components may be employed in optical computing andoptical signal processing.

What is needed is therefore are optical switches and optical logicdevices and method of implementing switching and optical logic at highdata rates. Combining these components into a system that is integratedonto a single substrate is also highly desirable.

SUMMARY OF THE INVENTION

One embodiment of the invention comprises an optical logic devicecomprising a laser, a pump, at least one optical input port, and atleast one optical output port. The laser comprises an optical resonatorand a gain region therein. The optical resonator comprisescounter-opposing microstructure-doped mirror portions. The gain regionis disposed between the mirror portion. The microstructure-doped mirrorportions are comprised of a plurality of microstructures disposed in anoptically transmissive structure. The pump is disposed with respect tothe optical resonator to pump the gain region. The at least one opticalinput port is disposed with respect to the optical resonator to couplelight into the gain region. The at least one optical output port isdisposed with respect to the optical resonator to couple light out ofthe gain region. The laser has at least a first state and a second statethat affect a characteristic of light coupled out the at least oneoptical output port. Light coupled into the at least one optical inputport switches the laser from the first state to the second state.

Another embodiment of the invention comprises an electrically tunableoptical logic device comprising a laser, a pump, a plurality ofelectrodes, at least one optical input port, and at least one opticaloutput port. The laser comprises an optical resonator and a gain regiontherein. The optical resonator comprises counter-opposingmicrostructure-doped mirror portions. The microstructure-doped mirrorportions comprise of a plurality of microstructures disposed in anoptically transmissive medium. At least a portion of the opticalresonator comprises electro-optic material having an index of refractionthat varies with applied electric field. The pump is configured to pumpthe gain region. The plurality of electrodes are arranged to apply anelectric field through the electro-optic material to vary the index ofrefraction. The optical resonator has an effective index of refractionthat can thereby be altered. The at least one optical input portdisposed with respect to the optical resonator to couple light into thegain region. The at least one optical output port disposed with respectto the optical resonator to couple light out of the gain region. Thelaser has at least a first state and a second state that affect acharacteristic of light coupled out of the at least one optical outputport. Light coupled into the at least one optical input port switchesthe laser from the first state to the second state. The electric fieldcreated by the electrodes alters the strength of at least one opticalmode supported by the optical resonator.

Another embodiment of the invention comprises a method of implementinglogic operations. This method comprising pumping a nanocavity lasercomprising an optical cavity and a light emitter in the optical cavity.The optical cavity is formed by reflective portions comprising an arrayof point structures. The nanocavity laser has an optical output that isdifferent for different states of the nanocavity laser. The methodfurther comprises inputting at least one optical signal into the opticalcavity to alter the state of the nanocavity laser thereby altering theoptical output of the nanocavity laser.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic drawing of an optical logic device comprising amultiple quantum well structure having an array of microstructuresdisposed therein to form an optical cavity.

FIG. 2 is a cross-sectional view of the optical logic device shown inFIG. 1 across the line 2-2 schematically illustrating themicrostructures in the multiple quantum well.

FIG. 3 is a cross-sectional view of an embodiment of the optical logicdevice that includes a quantum dot for emitting light and providingoptical gain.

FIG. 4 schematically illustrates an array of microstructures arranged inhexagonally closed-packed structure with a defect comprising amicrostructure having reduced size.

FIG. 5 schematically illustrates an electric field distribution in thehexagonally closed-packed structure depicted in FIG. 4.

FIG. 6 schematically illustrates an optical intensity distribution forthe hexagonally closed-packed structure depicted in FIG. 4.

FIG. 7 is a schematic drawing of an embodiment of the optical logicdevice showing microstructure-doped waveguide structures for couplinglight into and out of the optical cavity.

FIGS. 8A-8I schematically illustrate an exemplary process for formingthe optical logic device.

FIG. 9 schematically illustrates a microfluidic analysis system forsorting small light emitters suspended in a fluid.

FIG. 10 schematically illustrates microfluidic delivery of lightemitters to a microstructure-doped optical cavity.

FIG. 11 schematically illustrates a concentrated optical field in aregion of the optical cavity that traps a light emitter.

FIGS. 12A and 12B schematically illustrate an AND gate andimplementation of the AND operation using the optical logic device.

FIGS. 13A and 13B schematically illustrate an OR gate and implementationof the OR operation using the optical logic device.

FIG. 14 schematically illustrates a switch for switching an output onand off or for switching the wavelength of the output based on an inputto the switch.

FIG. 15 schematically illustrates a switch for controlling passage of aninput signal through the switch based on whether a pump signal isintroduced into the optical cavity.

FIGS. 16A and 16B schematically illustrate the operation of the switchshown in FIG. 15.

FIGS. 17A and 17B schematically illustrate a switch for switching thespatial direction of an input signal.

FIG. 18 schematically illustrates a NOT gate.

FIG. 19 schematically illustrates a NAND gate.

FIG. 20 schematically illustrates a NOR gate.

FIG. 21 schematically illustrates a flip-flop.

FIGS. 22A and 22B schematically illustrate an XOR gate andimplementation of the XOR operation using the optical logic device.

FIG. 23A is an exploded view of an embodiment of an electrostaticallytunable optical logic device that includes electro-optic material andelectrodes for applying an electric field through the electro-opticmaterial.

FIG. 23B is a cross-sectional view of the optical logic device depictedin FIG. 23A that schematically illustrates the microstructurescomprising electro-optic material disposed in the quantum wellstructure.

FIGS. 24A and 24B schematically illustrate an alternative contactarrangement.

FIG. 25 schematically illustrates a plurality of optical logic devicesand switches in an optical integrated circuit.

FIG. 26 schematically illustrates a plurality of optical logic devicesand/or switches in sufficient proximity to be in optical communication.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

These and other aspects, advantages, and features of the presentteachings will become apparent from the following detailed descriptionand with reference to the accompanying drawings. In the drawings,similar elements have similar reference numerals.

An optical logic device 10 having gain is schematically illustrated inFIG. 1. This optical logic device 10 comprises an ordered array 12 ofmicrostructures 14 disposed in a substantially optically transmissivemedium 16 comprising a quantum well structure. The opticallytransmissive medium 16 or quantum well structure is referred to as beingetched, with periodic microstructures 14 forming a microfabricatedtwo-dimensional Bragg mirror. More generally, the optically transmissivemedium is referred herein as being microstructured ormicrostructure-doped. This quantum well structure 16 is substantiallyoptically transmissive to the wavelength of operation of the device 10.The quantum well structure 16 comprises a plurality of layers 18 a, 18 bthat form wells (18 a) and barrier regions (18 b) as is well known inthe art. These well and barrier layers 18 a, 18 b provide light emissionwhen properly stimulated with energy, e.g., electrical current oroptical power.

In the embodiment depicted in FIG. 1, the microstructures 14 aredisposed in the layered quantum well structure 16 on opposite sides of acentral region 20. This central region 20 contains no microstructureforming a defect 21 in the array 12. The absence of a microstructure 14in the central region 20 creates an optical cavity 22, which is formedby counter-opposing portions 24 of the microstructure-doped opticaltransmissive medium 16. These microstructure-doped portions 24 arereferred to generally as microstructure-doped mirror or reflectorportions and may comprise Bragg mirrors or photonic bandgap mirrors asdiscussed more fully below. The mirror portions 24 of the optical cavity22 provide two-dimensional optical confinement and concentrates light inthe central region 20.

The central region 20 is also formed from the plurality of layers 18 a,18 b of the quantum well structure 16 and as a result provides opticalgain. Accordingly, this central region 20 is referred to as the gainregion. The optical cavity 22 supports optical modes that are resonantand thus concentrated in the gain region 20.

In various embodiments, the optical cavity 22 comprises an opticalnanocavity, an optical cavity having reduced dimension that supports fewoptical modes that can be fit into the reduced in dimension of thecavity. For example, the nanocavity can have a mode volume of betweenabout one tenth of a cubic half wavelength and ten times a cubic halfwavelength or between about 0.01 cubic micrometers and 1.0 cubicmicrometers. Similarly the gain region 20 in the optical cavity 22 mayvary be between about one atom and about 0.1 cubic micrometers involume. For 1.5 micrometer wavelength light, for example, the nanocavitymay have a lateral dimension of between about 100 nanometers to 500nanometers. The thickness of the perforated medium 16 may vary from onequarter of the wavelength of light in the optical transmissive medium toone wavelength of light in the medium. As will be discussed more fullybelow, reduced cavity size increases the switching and processingspeeds. Speeds between about 100 GHz and 200 GHz and even faster aretherefore possible. Reduced cavity size also decreases the number ofavailable modes which can reduce noise otherwise contributed by othermodes. Values outside the ranges described above are also possible.

In various embodiments, the array of microstructures 12 that form themirror portions 24 comprises photonic crystal. The microstructures 14are spatially arranged to produce a forbidden frequency region whereinlight within a specific band of wavelengths cannot propagate. Thisforbidden region corresponds to the light spectrum reflected by themirror portions 24. Accordingly, light is confined to the gain region 20by the surrounding mirror portions 24 where the light cannot propagate.The microstructures 14 are spatially arranged such that light within thegain region 20 that is incident on the array 12 is coherently scatteredso as to produce destructive interference within the mirror portions 24and beyond. The intensity of the light within the mirror portions 24therefore exponentially decreases with distance to the optical cavity.In contrast, the microstructures 14 are spatially arranged so as toproduce constructive interference within the gain region 20. In effect,the microstructures 14 act together as coherent Bragg scatterers,directing light back into the gain region 20.

In other embodiments, lateral confinement within the gain region 20 isprovided by lowering the effective index of refraction in the mirrorportions 24 of the optically transmissive structure 16. Themicrostructures 14 may, for example, be filled with air or vacuumproviding them with a refractive index lower than the medium 16, whichmay comprise, e.g., III-V semiconductor material. Material having arefractive index at least about 2.0 is preferred. Accordingly, theaverage refractive index of the mirror portions 24 in which themicrostructures 14 are located is less than the optically transmissivestructure 16. The gain region 20 has a relatively high refractive indexin comparison with the microstructured mirror portions 24 and as aresult optical energy is concentrated in this gain region.

Situating the gain region 20 in the optical cavity 22 forms a laser 26.An optical pump 28 pumps the gain region 20 from beneath the laser 26 inthe embodiment shown in FIG. 1. An arrow 30 represents a light beam thatpumps the gain region 20. This orientation is referred to asout-of-plane pumping as the pumping is not guided or propagated in-planealong the substantially transmissive structure 16. Instead, the pumpinglight is injected in a direction perpendicular to the substantiallytransmissive structure 16, which is shown as comprising a planarslab-like structure in FIG. 1.

As is well know, light output from lasers rapidly increases with a highcontrast when the gain medium is pumped above a threshold level.Accordingly, light represented by an arrow 32 is output from an outputport 34 of the laser structure 26. In addition, the optical logic device10 depicted in FIG. 1 includes first and second input ports 36, 38 thatreceive first and second optical input signals represented by arrows 40,42.

The optical output of the laser 26 depends on the first and secondoptical input signals 40, 42. In certain embodiments, for example, thepump 28 pumps the gain region 20 to a level below threshold. Light istherefore not emitted. If, however, the pump power 30 is supplemented bythe first and second input signals 40, 42 directed into the first andsecond input ports 36, 38, the gain region 20 is pumped above thresholdand light is emitted from the output port 34. Optical logic may beimplemented in this manner.

As described above, in certain embodiments the optical logic devices 10comprises a nanocavity device. The laser structure 26 comprises ananocavity laser wherein the optical cavity 24 is an optical nanocavitythat supports highly localized optical modes having reduced spatialdimensions. These spatial modes may be in the nanometer range.Nanocavity laser and laser devices are faster and less noisy than largerlasers. Optical cavities 22 having high cavity Q (higher finesse) alsopermit faster and high contrast (sharper) switching. The cavity Q mayrange between about 400 to 20,000 for example, about 10,000 in someembodiments although larger or smaller Q values may be used. Highcontrast optical logic gates may thereby be created.

A cross-sectional view of the logic device 10 is schematicallyillustrated in FIG. 2. The multiple quantum well structure 16 isdepicted as an elongated slab-like medium constructed from the pluralityof layers 18 a, 18 b arranged in a stack. The plurality of layers 18 a,18 b may comprises III-V semiconductor material such as for example,InGaAsP material. Other materials such as silicon, diamond, high indexoxide, or polymers may be used as well.

As shown, each of the microstructures 14 comprises an air-filled openingin the slab-shaped multiple quantum well structure 16. The size of thesemicrostructures 14 may vary with the specific application. In certainembodiments the size of the holes is between about ⅛ and ½ of thewavelength of operation of the devices 10 and the period of themicrostructures is between about ¼ and ¾ wavelength, although valuesoutside these ranges are possible. The absence of the microstructure 14that creates the defect produces a region between about ¼ to ¾wavelength across coinciding with the central region 20 described above.This central region 20 need not be in the center of the optical cavity22. The region may also be larger or smaller.

In some embodiments, for example, the size of the holes is between about300 nanometers and 500 nanometers and the period is between 400nanometers and 600 nanometers. The absence of the microstructure 14 thatcreates the defect produces a region between about 300 nanometers and600 nanometers across. Values outside these ranges, however, arepossible.

The type of microstructures 14 may vary. In one embodiment, themicrostructures 14 are holes extending deep into the slab-like structure16. In other embodiments, these holes may pass through the structure 16.The holes shown are cylindrical, and more specifically, have a shapecorresponding to a right circular cylinder. The shape of themicrostructures 14, however, is not so limited, rather themicrostructures can have other cylindrical and non-cylindrical shapes.For example, other cylindrical shapes having elliptical, square,rectangular, trapezoidal, and triangular, cross-sections are possible.These microstructure 14 may be formed, for example, by etching and mayhave sloped sidewalls and rounded corners. Accordingly, themicrostructures 14 may be less than perfectly shaped and may beirregular.

In still other embodiments, the microstructures 14 may be filled with amaterial other than air or vacuum. Preferably, this material has anindex of refraction substantially different than the substantiallytransmissive medium 16 in which they are formed. In various otherembodiments, the microstructures 14 may be covered over by one or morelayers of material.

In the case where the microstructures 14 together form a photonicbandgap crystal, the microstructures can be filled with a materialhaving a higher index of refraction than the optically transmissivestructure 16. The effective index of refraction within the effectivemirror portion 24 will be subsequently higher than the effective indexof refraction within the central region 20. However, the coherentscattering effect provided by the photonic bandgap crystal preventslight having a wavelength within a specific forbidden band frompropagating inside and thus through the mirror portions 34. Opticalmodes can therefore be concentrated to the gain region 20 even thoughthe gain region has a lower effective refractive index than the mirrorportions 34.

Since the microstructures 14 comprise a material having a differentrefractive index than the optically transmissive structure 16, themicrostructures will individually reflect and scatter light incidentthereon. Preferably, the spacing and specific arrangement of themicrostructures 14 provide the appropriate coherent effect to deflectlight of the desired wavelength back into the gain region 20. Suchphotonic crystal band gap structures are well known. The structuresdisclosed herein, however, need not be limited to conventional photoniccrystal band gap structures. Other types of mirrors 14, such as forexample concentric rings, concentric spheres, concentric cylinders, maybe employed. Mirrors 14 both well known as well as those yet to bedevised may be used.

As described above, in some embodiments the gain region 20 ischaracterized by an effective index of refraction which is higher thanan effective index of refraction within the mirror portions 24. Forexample, the air filled microstructures 14 have a lower index ofrefraction than does the quantum well structure 16 causing the averageand effective index in the mirror portions to be lower than the gainregion 20.

The degree to which the indices of refraction of the mirror portion 24and the gain region 20 differ from one another directly affects thestrength of confinement of light within the gain region and thus thespatial extent (i.e., cross-section) the optical modes therein. Higherindex contrast, i.e. larger differences between the two indices resultsin smaller optical modes. Photonic crystal mirrors are particularlyeffective at providing increased localization and reduced mode sizes. Asdiscussed above, nanocavity lasers, which have reduced size opticalcavities and optical modes, can be modulated at increased rates andpotentially reduced noise level. Accordingly, nanocavity device designsmay offer improved performance.

As described above, the optical mode is concentrated in the gain region20. The multiple quantum wells in the gain region 20 shown in FIG. 2 arepumped and may emit light as a result of such pumping. Optical energybuilds up in the optical cavity 22 and a portion of this optical energymay be released through the output port 34.

One embodiment of the optical logic device 10 that is schematicallyillustrated in FIG. 3 comprises a quantum dot 44 imbedded in theoptically transmissive structure 16 that is not a quantum wellstructure. This quantum dot 44 may comprise, for example, InGaAs/GaAsmaterials. Other materials III-V may be employed as well. The opticallytransmissive medium may comprise, e.g., glass or semiconductor. Inanother embodiment, for example, the quantum dot 44 may comprise PbS orHgTe and the optically transmissive structure 16 may comprise silicon.Other materials may be employed for the quantum dot 44 as well as forthe optically transmissive structure 16.

Other types of quantum dots 44 that may be employed include fluctuationquantum dots and self-assembled quantum dots. Self-assembled quantumdots are generally smaller in volume and offer higher confinementenergies. These quantum dots can as a result function at highertemperatures. In other embodiments, light emitting structures other thanquantum dots 44 may be disposed in the gain region 20. Examples includebut are not limited to a unit cell of a bulk crystal with dopants, arare-earth atom disposed in a crystal, or a free atom. Small lightemitters are particularly suitable for nanocavity devices.

The logic device shown in FIG. 3 also includes electrodes 46 disposed onopposite sides of the gain region for injecting current therethrough.Electronic pumping may thereby be accomplished. Alternatively, theelectrodes 46 may be on laterally disposed sides the perforated slab 16(e.g., on the left and right sides in FIG. 3). A continuous current pathis provided by the slab 16 such that the quantum dot 44 can be excitedby injecting current laterally through the slab.

Like the quantum well structure, this quantum dot 44 emits light whenenergized. When pumped above threshold, the laser structure 26 will emitlight through the output port 34.

The array 12 of microstructures 14 may also have differentconfigurations. In FIG. 4, for example, the microstructures 14 arearranged in a hexagonally closed-packed structure in the opticaltransmissive medium 16. These microstructures 14 form a photonic crystalnanocavity. In this optical nanocavity, the defect 21 comprises amicrostructure 14 with reduced size. The microstructures 14 along a row48 through the defect 21 are enlarged in comparison with the othermicrostructures in the array 12. Nevertheless, these microstructures 14comprise point structures arranged in an ordered array 12. In otherembodiments, square arrays and disordered arrays 12 of point structures14 may be employed. The microstructures 14 can also change size andshape, for example, in the central region 20. Such modifications may beemployed to control the laser frequency and quality (Q) and finesse ofthe cavity 22.

Although the defect 21 comprises a microstructure 14 having reducedsize, the defect may be formed by a microstructure 14 having increasedsize, and light will be localized in the optical cavity. More generally,the defect 21 is created by a perturbation in the array, which may be aphotonic crystal. This perturbation causes the localization of thelight.

FIG. 5 schematically illustrates an optical field distribution in theoptical nanocavity 22 based on modeling and simulating the hexagonallyclosed-packed array shown in FIG. 4. The electric field is concentratedin the gain region 20 of the optical nanocavity 22 where the defect 21is located. FIG. 6 is a near-field optical micrograph showing thedistribution of optical energy measured in the optical nanocavity 22.The optical energy is concentrated in a region 20 less than about twomicrometers in this photonic crystal nanocavity.

The optical output 32 as well as the first and second optical inputsignals 40, 42 may be coupled out of or into the optical cavity 22 viawaveguide structures. In the device 10 schematically illustrated in FIG.7, the optical first and second optical input ports 36, 38 comprisefirst and second waveguides portions 50, 52. The optical output port 34also comprises a waveguide portion 54. The device 10 further comprises apump port 56 for receiving pump radiation 30. This pump port 56 toocomprises a waveguide portion 58. In the embodiment depicted in FIG. 7,these waveguide structures 50, 52, 54, 58 are microstructure-dopedwaveguides that may comprise photonic crystal. In other embodiments, themicrostructure-doped waveguides 50, 52, 54, 58 are not photoniccrystals. Other types of waveguides including but not limited to channelwaveguides, rib or ridge waveguides, and strip-loaded waveguides may beemployed.

The first and second optical input signal 40, 42 as well as pump power30 propagate within the optically transmissive structure 16 within therespective waveguide portions 50, 52, 54 into the optical cavity 22 andto the gain region 20. Emission from gain region 20 is output from theoptical cavity 22 and propagates within the optically transmissivestructure 16 through the waveguide portion 54 for the output port 34.The first and second optical inputs 36, 38, the pump 56, and the output34 are referred to as in-plane as the input signals 40, 42, the pumpbeam 30, and the output signal 32 are propagated within and along theoptically transmissive structure 16. Vertical confinement may beprovided by the optically transmissive structure 16 which has a higherindex of refraction than a surrounding medium such that the light isguided within the optically transmissive structure.

An exemplary process for forming the optical logic device 10 is depictedin FIGS. 8A-8I. FIG. 8A schematically illustrates an InP substrate 60having InGaAs etch stop layer 62 formed thereon. An InP sacrificiallayer 64 is formed on the etch stop 62. A multilayer InGaAsP slab 66with four quantum wells is disposed on the InP sacrificial layer 64.This multilayer InGaAsP slab 66 may be formed by MOCVD in someembodiments although other processes may be employed.

This multilayer slab 66 may comprise more or less quantum wells.Similarly, other materials may be employed. For example, an alternativeexemplary embodiment, a multilayer structure 66 that comprisesGaAs/AlGaAs quantum wells is formed on AlAs. (The InP is replaced by theAlAs, and the InGaAsP is replaced by the GaAs/AlGaAs layers.) In anotherembodiment, an InAs/GaAs multilayer structure 66 is formed on AlAs. (TheInP is replaced by the AlAs, and the InGaAsP is replaced by InAs/GaAs.)In a different embodiment, a silicon structure 66 is formed on silicondioxide. (The InP is replaced by the silicon dioxide and the InGaAsP isreplaced by silicon.)

A silicon nitride (Si₃N₄) layer 68 is formed on the multilayer InGaAsPslab 66 as shown in FIG. 8B and a gold film 70 is formed on the siliconnitride layer 68 as illustrated in FIG. 8C. A PMMA layer 72 is formed onthe gold film 70 as shown in FIG. 8D. This PMMA layer 72 is patterned asillustrated in FIG. 8E. This pattern corresponds to the arrangement ofmicrostructures 14 in the array 12 of microstructure and can be orderedor disordered. The pattern also accounts for the gain region 20 byexcluding the formation of a microstructure 12 in that region. (In otherembodiments, the central region 22 may be etched for example to providean opening as the defect 21. A gain structure such as a quantum dot 44may be inserted that opening.)

As illustrated in FIGS. 8F, 8G, and 8H, the pattern is propagatedthrough the gold film 70, the silicon nitride layer 68 and into theInGaAsP slab 66. In this embodiment, holes corresponding to themicrostructure 12 are etched through the InGaAsP slab 66 to the InPsacrificial layer 64 immediately beneath. A portion of the InPsacrificial layer below the array 12 of microstructures 14 is removedusing a sacrificial etch as illustrated in FIG. 8I. An open area 74 isthereby formed in the InP sacrificial layer 64 immediately beneath thearray 12 of microstructures 14. Lower refractive index in this open area74 as well as possibly above the InGaAsP slab 66 provides for verticalconfinement of optical energy within the InGaAsP slab by total internalreflection. As discussed above, the optical cavity 22 provides lateralconfinement of optical modes in the gain region 20.

In certain embodiments, microstructures 14 are also formed to createmicrostructure-doped waveguide portions 50, 52, 54 as inputs 36, 38 andoutputs 34 to the laser structure. Conventional waveguides such aschannel, rib or ridge, or strip-loaded waveguides may be fabricated aswell.

Other processes and other materials may be employed. For example,quantum dots 44 may be embedded in the central region slab 66 asdescribed above. These quantum dots 44 may be formed, for example, bymolecular beam epitaxy (MBE). The position of the quantum dots maycontrolled by performing selective growth on masked substrates althoughother methods may be employed.

Small structures such as quantum dots or fluorescent beads may beindividually selected, e.g., to match the wavelength of a mode supportedby the optical cavity 24 and may be inserted in the gain region 20. FIG.9 schematically illustrates a microfluidic analysis system 700 forsorting small light emitters 702 suspended in a fluid 704. The system700 includes an input flow channel 706, an observation channel 708, anda sorting region 100. The sorting region 100 includes first and secondvalves 712, 714 as well as first and second output flow channels 716,718.

The input flow channel 706 is connected to the observation channel 708which has smaller dimensions. The observation channel 708 is connectedto the first and second valves 712, 714 each of which may be open orclosed. The first and second output flow channels 716, 718 are connectedto the first and second valves 712, 714, respectively. Opening the firstvalve 712 provides a path from the observation channel 708 to the firstflow channel 716. Opening the second valve 714 provides a path from theobservation channel 708 to the second flow channel 718.

The input flow channel 702 may be connected to a source or reservoir(not shown) containing fluid with many small light emitters therein. Apump (also not shown) may be connected to the input flow channel 706 andthe reservoir. The fluid can also be designed to flow through surfacetension if the walls of the flow channel are hydro-philic, or byelectro-osmotic pumping. The system 700 may further comprise a lightsource 720, as well as collection optics 722 and a detection system 724,disposed with respect to the observation channel 708.

This microfluidic analysis system 700 may operate similar to aFluorescence Activated Cell Sorter (FACS). Light emitters 702 from thereservoir are passed through the input flow channel 706 into theobservation channel 708 to be processed. The pump facilitates flow ofthe light emitters 702. A neck portion 726 of the input channel 726together with the reduced dimension of the observation channel 708permits individual light emitters 702 to be isolated for study in theobservation channel.

Light emitters 702 may be sorted, for example, based on the wavelengthof light emitted in response to illumination from the light source 720.As shown in FIG. 9, an excitation beam 728 incident on one of the lightemitters 702 causes the light emitter to radiate light at a particularwavelength. This wavelength may depend on properties of the lightemitter 702 such as size and composition. The radiation emitted from thelight emitter 702 is collected by the collection optics 722 and can beused to identify the type of emitter. The light emitter 702 is directedinto either the first or second output channel 716, 718 by properlysetting the first and second valves 712, 714.

The first and second output channels 716, 718 may continue ontoadditional channels similar to those shown in FIG. 9 for furtherscreening or to other destinations. Screening may be based on wavelengthand/or other optical or non-optical properties. Other variations of thesorting system 700 and methodology are also possible.

In certain embodiments, the light emitters 702 are flowed into a flowchannel 730 disposed above a microstructure-doped optical cavity 732formed by opposing microstructure-doped mirrors portions 734 as shown inFIG. 10. Optical tweezing can be used to appropriately position thelight emitter 702 in the optical cavity 732. The light emitter 702,which preferably has a higher index of refraction than that of thesurrounding medium, is drawn into a central region 736 of the opticalcavity 732 where optical intensity is concentrated as illustrated inFIG. 11. The light emitter 702 may be optically trapped in this centralregion 736. Advantageously, the light emitter 702 may be situated at thelocation 736 of a strong optical mode supported by the optical cavity732. The light emitter 702 will provide gain for the resonant cavity732.

The light emitter 702 may comprise a bead or quantum dot that is sortedas described above. Exemplary beads may have a lateral dimension ofabout 60 nanometers although the beads may be larger or smaller. Otherstructures may also be used as light emitters 702. Examples ofstructures that may be employed include but are not limited tofluctuation quantum dots, self-assembled quantum dots, a unit cell ofbulk crystal, a rare-earth in a crystal, free atoms or luminescentmolecules. Exemplary quantum dots include colloidally suspended HgTe,PbS, CdSe or CdS, which may be microfluidically delivered to silicon oninsulator nanocavities.

Both active and passive cavities 732 may produce the field for opticaltrapping. For example, in one embodiment, the optical trapping field isgenerated by gain from the quantum wells comprising themicrostructure-doped photonic crystal mirrors 734. Current injected intothe quantum wells may produce a localized optical intensity distributionin the optical cavity 732. This type of cavity 732 is referred to hereinas an active cavity. In another embodiment, the optical trapping fieldis provided by an external input light source matched to the frequencyof one of the cavity modes. Light from this external source is injectedinto the cavity 732 to provide the concentrated optical field. A siliconon insulator medium is an example of such a passive cavity 732.

As described above other techniques may be employed to fabrication thelaser structures and optical logic devices 10.

The optical logic device 10 described above may be used as an AND gate100 such as shown in FIG. 12A. The AND gate 100 has first and secondinputs 102, 104 and an output 106. A signal is output from the AND gate100 only when signals are received by both the first and second inputs102, 104.

To implement this logical operation using the optical logic device 10described above, pumping may be sufficiently below threshold that lasingoccurs upon introduction of both first and second signals into theoptical cavity 22 and not with solely the first input signal or solelythe second input signal. FIG. 12B illustrates this concept graphically.FIG. 12B schematically shows the threshold level of power 108 whichcauses the laser 26 to lase and output to be emitted from the opticallogic device 10. FIG. 12B also schematically illustrates the pump powerlevel 110 as well as the first and second input signal levels 112, 114.Each of these signals power levels 112, 114 are less than the thresholdlevel 108. Moreover, the combination of the first input and the pump(represented by level 116) is also less than the threshold 108 forlasing. Similarly, the sum of the second input and the pump (representedby level 118) is less than the threshold 108. The combination of thefirst and second inputs together with the pump (represented by level120), however, is larger than threshold 108 such that the laser 26 lasesupon introduction of both the first and second optical input signalswhile the laser 26 is being pumped.

The optical logic device 10 may also be used as an OR gate 130 such asshown in FIG. 13A. The OR gate 130 also includes first and second inputs132, 134 and an output 136. A signal is output from the OR gate 130 whensignals are received by either the first and second inputs 132, 134.

To implement this logical operation using the optical logic device 10described above, pumping may be below but relatively close to thresholdsuch that lasing occurs upon introduction of either first and secondsignals into the optical cavity 22. FIG. 13B illustrates this conceptgraphically. FIG. 13B schematically shows the threshold level 138, aswell the pump power level 140 and the first and second input signalslevel 142, 144. Although the pump level 140 is below threshold 138, thefirst input signal together with the pump (represented by level 146) andthe second input signal together with the pump (represented by level148) are above threshold 138.

Advantageously, the nonlinear intensity response in lasers as a resultof lasing threshold characteristics provides high contrast for thesegates 100, 130. Additionally, the logical device 10 can be reconfiguredto operate as an AND or an OR gate depending on the level of pumping.The lower level of pumping can be used to implement the AND operationwhile the higher level of pumping may be used implement the OR function.Other designs are possible. For example, the AND and OR gates 100, 130may comprise more inputs than the first and second inputs 102, 104, 132,134 and the more than one output 106, 136. For example, three or moreinputs may be ANDed together and the AND gate 100 may have two or moreoutput.

The optical logic device 10 may also be used as an optical switch 150such as shown in FIG. 14. The switch 150 includes a signal input 152 andan output 154. In one embodiment, the switch 150 produces an outputsignal when a signal is applied to the input 152.

To implement this switching operation using the optical logic device 10described above, the optical cavity 22 is pumped so as to produce lightemission from the emitter in the gain region 20. The optical cavity 22,however, is not tuned to the wavelength of emission such that an opticalresonance is not achieved and output is not obtained for thatwavelength. Introduction of light into the input 152 may, however,through nonlinear effects such as carrier-induced changes cause an indexof refraction variation in the optical cavity 22. This index variationtunes the cavity 22 to the frequency of light emitted by the lightemitter in the gain region 20. Optical resonance and optical output fromthe laser device 26 will be obtained.

Conversely, the optical cavity 22 may be tuned to the wavelength ofemission of the light emitter in the gain region 20 such that an opticalresonance is achieved and output is obtained for that wavelength.Introduction of light into the input 152 may, however, through nonlineareffects cause an index of refraction variation in the optical cavity 22that detunes the cavity away from frequency of light emitted by thelight emitter in the gain region 20. Optical output from the laser 26would cease.

In other embodiments, inducing index of refraction variation maysuppress or change the spatial extent or polarization of an optical modeotherwise supported by the optical cavity thereby attenuating outputwithout necessarily altering the resonant frequency of the opticalresonator 22. The relative Qs of the modes in a laser cavity 22 can bechanged by selectively altering the losses in these modes through theoptical or electronic injection of excess carriers. Addition orsubtraction of such carriers can contribute to transparency and reduceabsorption losses, or can modify the refractive index of the mirrorsencountered by light in the competing modes. Q-switching between onelasing mode and another mode may be accomplished in this manner and mayyield even faster switching responses.

In one embodiment, for example, the optical switch 100 comprises acavity that supports two competing modes. The first mode has a firstpolarization and the second mode has a second polarization. The relativeloss of these two modes may be altered by applying a signal to theinputs 102, 104 as described above. The polarization of the output ofthe switch 100 will vary depending on which mode dominates. The outputmay thus be switched between polarizations. In some embodiments, apolarizer or other polarization sensitive component is included with theoptical cavity 22. The output of the switch 100 may thus be turned on oroff.

As illustrated above, this switch 150 may be configured to operate as aNOT gate. An optical signal is output from the switch 150 when nooptical signal is applied to the input 152. However, when an opticalsignal is introduced to the input 152, the output of the switch is null.In the polarization-based switch 100 described above, a NOT gate isobtained by selecting the polarizer to block the polarization outputwhen the input is applied.

In an alternate related embodiment, the optical cavity 22 is tuned to afirst wavelength when no light is introduced into the input 152 and istuned to a second wavelength when light is introduced into the input.Light emission produced by pumping the gain region 20, however, includesboth the first and second wavelengths. The switch 150 will thereforeoutput light having the first wavelength or light having the secondwavelength depending whether a signal is applied to the input 152.

High cavity Q's and high finesses increase contrast in these switches150. Use of optical nanocavities may further enhance the performance. Areduction in the cavity volume limits the number of modes and therebyyields faster switching, as the efficiency of the coupling ofspontaneously emitted light into the modes supported is increased. Forexample, the spontaneous emission rate into a certain mode from anemitter in a cavity may be proportional to Q/V where Q is the qualityfactor of the cavity and V is the volume of the cavity.

In other embodiments, the optical pump is used as an input to controlthe output. See, for example, FIG. 15. This switch 160 includes a signalinput 162, a pump/input 164, and an output 166. A signal applied to thesignal input 162 is output from the switch 160 when the optical cavity22 is sufficiently pumped.

FIGS. 16A and 16B schematically illustrate how the pump 164 prevents thesignal input into the switch 160 from being output by the switch. FIG.16A shows an array 172 of microstructures 174 forming an optical cavity176 and a gain region 178 in the optical cavity that includes a quantumdot 180 therein. An optical signal (represented by an arrow 182) thatdoes not excite the quantum dot 180 is input into the optical cavity176. This optical signal 182 may, for example, have a wavelength shorterthan any optical transition in the quantum dot 180. The quantum dot 180remains in the ground state. In this embodiment, the optical cavity 176is tuned to the wavelength of the optical signal 182, and thus, theoptical signal passes though the optical cavity 176 which acts as aFabry-Perot filter.

Introducing a pump beam (represented by an arrow 184) into the opticalcavity 176 excites the quantum dot 180 as shown in FIG. 16B. In thisembodiment, the pump beam 184 has wavelength at least as large as anoptical transition of the quantum dot 180. Exciting the quantum dot 180induces an index of refraction variation in the optical cavity 176 andthereby detunes the cavity away from the wavelength of the input signal182. The input signal 182 is thus not transmitted through the opticalcavity 176 and not output from the switch 160.

The pump 164 may be employed as an input to actively control whether theswitch 160 is on or off. In certain embodiments, for example, the pumpsignal 184 may itself be controlled by logic components to implementmore complex logic operations.

Another type of switch 190 is depicted in FIG. 17A. This switch 190includes a signal input 192 as well as first and second outputs 194,196. Light is output from either of the first and second outputs 194,196 depending on whether a signal is applied at the input of the switch190.

Asymmetry in an array 212 of microstructures 214 such as shown in FIG.17B produces first and second optical modes that propagate in differentdirection. In this embodiment, the asymmetry is established by aplurality of elongated microstructures 216 in an optical cavity 218 ator near a gain region 220 therein. The gain region 220 is pumped withpump energy (represented by an arrow 222) providing optical energywithin the optical cavity 218. Without application of an input signal(represented by an arrow 224), the optical energy is in the firstoptical mode which dominates. Introducing the input signal 224 into theoptical cavity causes refractive index variation altering the opticalproperties of the cavity 218. The optical cavity 218 preferentiallysupports the second optical mode over the first optical mode. The firstoptical mode which propagates in a first direction (represented by anarrow 226) through the first output 194 is suppressed while the secondoptical mode which propagates in a second direction (represented by anarrow 228) through the second output 196 is enhanced.

This switch 190 may also be employed as a NOT gate. For example, lightemerges from the first output 194 when no optical signal is applied tothe input 192. Conversely, the first output 194 is null when an opticalsignal introduced into the input 192.

A schematic illustration of a NOT gate 230 is depicted in FIG. 18. Anoptical NAND gate 240 may be formed by coupling the output of an opticalAND gate 242 with the input of an optical NOT gate 244 as shown in FIG.19. Similarly, an optical NOR gate 250 may be formed by coupling theoutput of an optical OR gate 252 with the input of an optical NOT gate254 as shown in FIG. 20.

An optical flip flop 600 can also be constructed by employing theoptical logic devices described above as shown in FIG. 21. The flip-flop600 may be formed, for example, from first and second NOR gates 610, 620each comprising an OR gate 602 followed by a NOT gate 604. The first NORgate 610 has first and second inputs 612 a, 612 b and an output 614.Similarly, the second NOR gate 620 has a first and second inputs 622 a,622 b and an output 624. The second input 612 b of the first NOT gate610 is optically connected to the output 624 of the second NOR gate 620.Similarly, the second input 622 b of the second NOT gate 620 isoptically connected to the output 614 of the first NOR gate 610.

In FIG. 21, the inputs 612 a, 622 a to the first and second NOR gates610, 620 corresponds to SET and RESET of the flip-flop 600,respectively. The outputs 614, 624 of the first and second NOR gates610, 620 correspond to Q and Q. As with conventional flip-flops, when asignal is applied to SET the flip-flop, Q and Q are high (1) and low (0)respectively. Even after the SET signal is removed such that the SET is0, Q and Q remain 1 and 0. The flip-flop 600 thus has memory. Also aswith conventional flip-flops, when a signal is applied to RESET theflip-flop, Q and Q are switched to low (0) and high (1) respectively.Even after the RESET signal is removed such that the RESET is 0, Q and Qremain 0 and 1, respectively.

The optical flip-flop 600, however, is fabricated using laser devicessuch as described herein, and the inputs 612 a, 622 a as well as theoutputs 614 and 624 are optical. The connection between the inputs 612b, 612 a and the outputs 614 and 624 are also optical. These opticalconnections may be implemented by using waveguides such asmicrostructure-doped waveguides (e.g., within the photonic crystal) orconventional waveguides (e.g., channel, rib or ridge, or strip loadedwaveguides). Other approaches may be employed to form the opticalconnection. The OR and NOT gates 602, 604 comprise microstructure-dopedlaser structures. Nanocavity laser structures offer increased switchingrates, high contrast, and reduced noise, all of which are desirable in asingle-bit optical storage element. Although the flip-flop 600 isoptical, the flip-flop provides memory. The flip-flop 600 may thus beused as a buffer or memory device. Other configurations and designs,however, are also possible.

The optical logic device 10 may also be used as an XOR gate 260 such asshown in FIG. 22A. The XOR gate 260 includes first and second inputs262, 264 and the output 266. A signal is output from the XOR gate 260when a signal is received by solely the first input 262 or by solely thesecond input 264 but not when signals are received at both the first andsecond inputs.

To implement this logical operation using the laser-based optical logicdevice described above, the pump power introduced into the gain region20 is below but relatively close to threshold such that lasing occursupon introduction of either first and second signals into the gainregion. This threshold is identified as Threshold 1 (268) in FIG. 22B,which illustrates this concept graphically. FIG. 22B also schematicallyillustrates the pump power level 270 as well as the first and secondinput signal levels 272, 274. Although the pump level 270 is below thethreshold 268 for lasing, the combination of the first input and thepump (represented by level 276) is above threshold. Similarly, thecombination of the second input and the pump (represented by level 278)is above the threshold 268.

The pump power is sufficiently high, however, that the sum of the firstand second inputs together with the pump (represented by level 280) isabove a second threshold 282. At or above this second threshold 282, theoptical energy in the gain region 20 induces a refractive indexvariation that alters the modes supported by the optical cavity 22. Forexample, the optical cavity 22 may be detuned such that the wavelengthof the light emitter in the gain region 20 is not the same as theresonant frequency of the optical cavity. In other embodiments, theoptical mode supported by the optical cavity 22 is suppressed. Theoutput of the XOR gate 260 is thus null when both these first and secondoptical signals are applied to the inputs 262, 264 of the gate.

The optical cavity can additionally be tuned or switched electrically aswell as optically. In one embodiment schematically illustrated in FIG.23A, for example, a laser structure 300 comprising an array 302 ofmicrostructures 304 in an optically transmissive structure 306additionally comprises electro-optic material. As discussed above, themicrostructures 304 disposed in the optically transmissive structure 306form an optical cavity 308 with a gain region 310 therein. The laserstructure 300, however, also includes electrodes 312. This device 300 iselectrostatically tunable. A voltage source 314 may be electricallyconnected to the electrodes 312 to induce an electric fieldtherebetween. As illustrated in FIG. 23B, the microstructures 304 maycomprise the electro-optic material. The electrodes 312 are disposedsuch that the electric field passes through this electro-optic material.The electro-optic material may comprise a nonlinear or electro-opticpolymer although other types of nonlinear materials may be used.Application of the electric field through the electro-optic materialcauses the refractive index of the electro-optic material andconsequently that of the optical cavity 308 to vary. As discussed above,refractive index variation may tune or detune the optical cavity 308 orotherwise alter the modes that are supported by the cavity. The electricfield could thus be used to suppress or enhance particular opticalmodes.

An alternative configuration for electroding is depicted in FIG. 24A,which shows a microstructure-doped laser structure 800 comprising aquantum well structure having holes 802 formed therein. In thisembodiment, the quantum well structure 800 comprises layers of InGaAsP803. The quantum well structure 800 is mounted on a support 804 that isformed on a substrate 806. The support 804 and substrate 806 bothcomprises InP. An open region 808 surrounds the support 804. The support804 is formed from a sacrificial layer deposition and sacrificial etchas discussed more fully below. Accordingly, an etch stop layer 810 isdisposed between the support 804 and the substrate 806. An electricalcontact 812 is formed with the quantum well structure 800. Thiselectrical contact 812 may comprise metal or metal alloy such as forexample Au/Zn. The electrical contact 812 is electrically isolated by aninsulating layer 814. This insulating layer 814 may comprise aninsulator such as polyimide. Another contact (not shown) may be formedto the substrate.

In certain embodiments, the microstructure-doped laser structure 800 isformed by etching through the multiple quantum well layers 803 and intothe sacrificial InP. A sacrificial etch removes InP beneath themicrostructure-doped laser structure 800. The microstructures 802 areformed in the multiple quantum well layers 803 and metallization isdeposited and patterned to create the contact 812. The intervening layerof polyimide 814 is formed prior to the metallization. Other methods maybe employed to form the microstructure-doped laser structure 800.

An SEM image of the resultant nanolaser device is shown in FIG. 24B. Avoltage may be applied between the contact 812 and the substrate 806 tocreate an electric field in the multiple quantum well structure 800.Depending on the design, this electric field may be employed to tune anoptical cavity in the structure 800 as described above or toelectrically pump the laser structure. Other designs are also possible.

Optical logic devices 400 and optical switches 402 may be combinedtogether to yield more sophisticated structures as shown in FIG. 25. Forexample, an output 404 of a first optical logic or switching element 406may be optically coupled to an input 408 of a second optical logic orswitching element 410. Similarly, an output 412 of the second opticallogic or switching element 410 may be optically coupled to an input 414of a third optical logic or switching element 416 and so on. The opticallogic devices 400 and optical switches 402 may have one or more inputports 418 and/or one or more output ports 420. Optical connections maybe formed with waveguides 422 coupled to the input and output ports 418,420. These waveguides 422 may comprise microstructure doped waveguidescomprising microstructures formed in an optically transmissive medium.Alternatively, these waveguides 422 may comprise other types ofwaveguides including but not limited to channel waveguides, rib or ridgewaveguides, strip loaded waveguides, etc.

The optical logic devices 400 and optical switches 402 may be integratedtogether monothically on an optical integrated circuit (IC) 424 or chipor portion thereof. These structures 400, 402 may for example be in oron a substrate (not shown) that may or may not have one or more layers(not shown) formed thereon. The substrate may for example comprise InPand multiple layers of III-V material may be formed thereon.Microstructures may be formed in the multiple layers to form the opticallogic devices 400 and optical switches 402 and possible opticalwaveguides that provide optical interconnection as described above. Inother embodiments, the substrate may comprise silicon and themicrostructures may be formed therein. In some embodiments silicon oninsulator may be employed. Other materials may be used as well.

Additional optical components 426 such as detectors and laser sourcesmay also be included and may be optically connected to one or more ofthe optical logic devices 400 or switches 402. Optical as well aselectrical connectors (not shown) may also be included to provideoptical or electrical connection. Optical beams may be coupled in-planefrom the sides of the monolith structure 424 as well as out-of-plane asdescribed above. In certain embodiments, pumping may be channeledthrough the monolith structure 424 and distributed to a plurality ofoptical devices 400 or switches 402. A pumping source (not shown)external to the monolith structure 424 may be employed.

A network 428 of optical logic devices 400 and/or switches 402 may beinterconnected together, for example, to provide optical signalprocessing, to route voice or data signals, to perform computation, etc.In various embodiments, the optical signals will comprise pulses coupledto the switches and logic devices. These pulses may reach differentswitches 402 and devices 400, 426 at different times as a result in partof different distances that the pulses travel. Advantageously, incertain embodiments waveguide portions 422 that comprise photoniccrystal may be used to control the timing of the pulses. By varyingcharacteristics such as spacing and arrangement of the microstructuresin photonic crystal waveguide portions 422, optical dispersion may becontrolled. Accordingly, the pulses may be propagated through waveguideportions 422 at different speeds depending on the direction of the pulsewith respect to the photonic crystal and the relative amount ofdispersion. This amount of dispersion may additionally depend on thewavelength and the distance to be traveled as well as the direction ofpropagation of the light through the photonic crystal. In certaindirections, light can be collimated and propagate at close to the speedof light in the photonic crystal structure. In other direction, lightcan be slowed down by approximately 10 times. The waveguides portions422 in the network 428 therefore may be configured to provide the propertiming by controlling the propagation speed of the pulse and thedistance traveled.

Additionally, to prevent feedback that may degrade performance of thelaser structures, the optical logic devices 400 and switches 402 may bedesigned to output a different wavelength than are input into therespective optical cavity. For example, the first output 404 of thefirst optical logic or switching element 406 may be a signal at a firstwavelength which is coupled to the input 408 of the second optical logicor switching element 410. The output 412 of the second optical logic orswitching element 410 may be a signal at a second wavelength which isoptically coupled to the input 414 of the third optical logic orswitching element 416. Backscatter from the optical logic or switchingelements 406, 410, 416 or from the waveguides 422 or as a result of thecoupling therebetween may produce a return signal that may enter theoptical cavity of the optical logic or switching elements. For example,a portion of the output signal from the second optical logic orswitching element 410 may be returned back to the optical cavity of thatelement. If the input signal that activates this element 410 is adifferent than the output signal, possible having a shorter wavelength,the portion of the output signal returned to the second optical logic orswitching element will less likely interfere with the operation of theelement. Other variations in the design and operation of the opticalintegrated circuit 424 are possible.

FIG. 26 schematically illustrates one example of a plurality of lasercavities 510 integrated together monolithically. A hexagonallyclosed-packed array 512 of microstructures 514 is formed in a matrixmedium 516 that is optically transmissive to the wavelength orwavelengths of operation. Five optical cavities 510 are shown formedwhere microstructures 514 in the array 512 are absent. The five opticalcavities 510, however, are in close proximity to provide opticalcommunication therebetween. For example, light from a first opticalcavity 510 a may be coupled to a second optical cavity 510 b and lightfrom the second optical cavity can be coupled to a third optical cavity510 c or vice versa. In this example, the separation of the opticalcavities 510 may be between about 1 micrometers and 100 micrometers,although the separation may be outside this range. In various preferredembodiments, however, separation less is than the coherence length oflight emitted from the laser cavities 510. In this or other embodiments,light from the optical cavity 510 may be focused, collimated, or guidedto facilitate coupling to another optical cavity or elsewhere.Diffractive losses may be reduced since light beams exiting the cavity510 and propagating through the matrix 516 do not encounter a largechange in refractive index that would introduce optical diffraction outof the plane of the patterned matrix 516.

Massive integration is thus possible. For example, between about 100 and1,000,000 optical devices and/or switched may be integrated together ona chip. The devices and switches may be between about 0.5 micrometersand 1 micrometers in size and may be separated by between about 1micrometers and 100 micrometers with or without the use of waveguides.Values outside these ranges are possible.

Moreover, using laser structures for optical logic and switching permitsgain to be introduced to the optical signals. Likewise a series of logicgates and switches may be cascaded and the signal may be propagated adistance. Attenuation resulting from loss can be mitigated by this gain.

Accordingly, compact, robust and efficient optical logic and switchingsystems can be assembled that offer both high speed and high contrast.Radically new system architectures may be enabled, for example, by theoptical logic devices and switches, which may be reconfigured asdescribed above. All optical processing, routing, and computing may beimplemented. Other applications are possible as well.

The structures and methods may vary from those specifically describedherein. For example, the pumping of gates and other logic devices may beemployed as an input to actively control the optical logic device. Thepump signal directed to logic devices may itself be controlled byswitches or logic components to implement more complex operations. Also,the input need not all be optical. For example, an AND gate can have oneoptical input and one electrical input that are ANDed together. Othervariations in the optical logic device and switches and method ofimplementing the optical logic and switching are also possible.

The methods which are described and illustrated herein is not limited tothe exact sequence of acts described, nor is it necessarily limited tothe practice of all of the acts set forth. Other sequences of events oracts, or less than all of the events, or simultaneous occurrence of theevents, may be utilized in practicing the embodiments of the invention.Additionally, although the invention has been disclosed in the contextof certain embodiments and examples, it will be understood by thoseskilled in the art that the invention extends beyond the specificallydisclosed embodiments to other alternative embodiments and/or uses andobvious modifications and equivalents thereof. Accordingly, theinvention is not intended to be limited by the specific disclosures ofpreferred embodiments herein.

1. An optical logic device comprising: a laser comprising an opticalresonator and a quantum dot therein, said optical resonator comprisingcounter-opposing microstructure-doped mirror portions, said quantum dotdisposed between said mirror portions, said microstructure-doped mirrorportions comprising of a plurality of microstructures disposed in anoptically transmissive structure; an optical pump disposed with respectto said optical resonator to pump said quantum dot; at least one opticalinput port to couple light into said laser; and at least one opticaloutput port to couple light out of said laser; wherein said laser has atleast a first state and a second state that affect a characteristic oflight coupled out said at least one optical output port, light coupledinto said at least one optical input port switching said laser from saidfirst state to said second state.
 2. The optical logic device of claim1, wherein said plurality of microstructures comprises an ordered arrayof point structures or a disordered array of point structures.
 3. Theoptical logic device of claim 2, wherein said point structures compriseholes in said optically transmissive structure.
 4. The optical logicdevice of claim 2, wherein said microstructure-doped mirror portionscomprise photonic crystal mirrors.
 5. The optical logic device of claim1, wherein said optical cavity has a mode volume between about 0.01cubic micrometers and about 1.0 cubic micrometers.
 6. The optical logicdevice of claim 1, wherein said optically transmissive structurecomprises silicon-based material.
 7. The optical logic device of claim1, wherein said optically transmissive structure comprises silicon. 8.The optical logic device of claim 1, wherein said at least one opticalinput port comprises an optical waveguide.
 9. The optical logic deviceof claim 8, wherein said optical waveguide comprises amicrostructure-doped waveguide.
 10. The optical logic device of claim 9,wherein said optical waveguide comprises photonic crystal waveguidestructure.
 11. The optical logic device of claim 1, wherein said atleast one optical output comprises an optical waveguide.
 12. The opticallogic device of claim 11, wherein said optical waveguide comprises amicrostructure-doped waveguide.
 13. The optical logic device of claim12, wherein said optical waveguide comprises photonic crystal waveguidestructure.
 14. The optical logic device of claim 1, wherein said lightcoupled out said at least one optical output port has a longerwavelength than said light coupled into said at least one optical inputport.
 15. The optical logic device of claim 1, wherein said opticallytransmissive structure comprises a polymer material and saidmicrostructures comprise holes in said polymer material.
 16. The opticallogic device of claim 15, wherein said quantum dot comprises III-Vsemiconductor material.
 17. The optical logic device of claim 16,wherein said III-V semiconductor material comprises InGaAsP material.18. The optical logic device of claim 15, wherein said polymer materialcomprises a photorefractive material.
 19. The optical logic device ofclaim 18, wherein said light coupled into said at least one opticalinput port switching said laser from said first state to said secondstate causes a photorefractive change in the effective index ofrefraction of said optical resonator to switch said laser from saidfirst state to said second state.
 20. The optical logic device of claim1, wherein said optical resonator is tuned to the wavelength of lightemitted by said quantum dot while in the first state, while said opticalresonator is not tuned to the wavelength of light emitted by saidquantum dot while in the second state.
 21. The optical logic device ofclaim 1, wherein said optical resonator supports a principal mode havinga first spatial extent or polarization while in the first state, andsaid optical resonator supports a principal mode having a second spatialextent or polarization while in the second state.
 22. The optical logicdevice of claim 1, wherein said optical resonator is tuned to a firstwavelength while in the first state and said optical resonator is tunedto a second wavelength while in the second state, said quantum dot beingconfigured to emit both the first and second wavelengths when pumped.23. The optical logic device of claim 1, wherein said optical resonatorsupports a first principal mode that propagates in a first direction toa first optical output port while in the first state, and wherein saidoptical resonator supports a second principal mode that propagates in asecond direction to a second optical output port while in the secondstate.
 24. The optical logic device of claim 1, wherein said first statecomprises optical energy being present at said optical output port andsaid second state comprises substantially no optical energy beingpresent at said optical output port.
 25. The optical logic device ofclaim 1, wherein said at least one optical input port and said at leastone optical output port are in-plane with respect to the optical logicdevice.
 26. A network of optical logic devices comprising two or moreinterconnected instances of the optical logic devices of claim
 1. 27.The optical logic device of claim 1, wherein said quantum dot comprisesIII-V semiconductor material.
 28. The optical logic device of claim 27,wherein said III-V semiconductor material comprises an InGaAs material.29. The optical logic device of claim 1, wherein said mirror portionscomprise silicon, glass, diamond, a high refractive index oxide, or apolymer.
 30. The optical logic device of claim 1, wherein said mirrorportions comprise a photorefractive or electro-optic material.
 31. Theoptical logic device of claim 1, wherein said quantum dot has saidmirror portions on at least four sides.
 32. The optical logic device ofclaim 1, wherein said quantum dot is configured to emit light of aselected wavelength and said microstructure-doped mirror portionscomprise a material substantially transparent to the selectedwavelength.
 33. An optical logic device comprising: a laser comprisingan optical resonator and a gain region therein, said optical resonatorcomprising counter-opposing microstructure-doped mirror portions, saidgain region disposed between said mirror portions, saidmicrostructure-doped mirror portions comprising of a plurality ofmicrostructures disposed in an optically transmissive structure; a pumpdisposed with respect to said optical resonator to pump said gainregion; at least one optical input port disposed with respect to saidoptical resonator to couple light into said gain region; and at leastone optical output port disposed with respect to said optical resonatorto couple light out of said gain region; wherein said laser has at leasta first state and a second state that affect a characteristic of lightcoupled out said at least one optical output port, light coupled intosaid at least one optical input port switching said laser from saidfirst state to said second state and wherein said optically transmissivestructure comprises a quantum well structure and said microstructurescomprise holes in said quantum well structure.
 34. The optical logicdevice of claim 33, wherein said quantum well structure comprises III-Vsemiconductor material.
 35. The optical logic device of claim 34,wherein said III-V semiconductor material comprises InGaAsP material.36. The optical logic device of claim 33, wherein said gain regioncomprises a quantum dot.
 37. The optical logic device of claim 33,wherein said pump comprises an optical pump.
 38. A laser optical logicdevice comprising: a laser comprising a quantum dot comprising a firstmaterial and configured to emit light of a selected wavelength, saidquantum dot having microstructure-doped mirror portions on at least foursides, said mirror portions comprising a second material that issubstantially transparent to the selected wavelength, said lasercomprising said mirror portions; a pump disposed with respect to saidquantum dot to pump said quantum dot; at least one optical input port tocouple light into said laser; and at least one optical output port tocouple light out of said laser; wherein said laser has at least a firststate and a second state that affect a characteristic of light coupledout said at least one optical output port, light coupled into said atleast one optical input port switching said laser from said first stateto said second state, and wherein said first material comprises PbS orHgTe and said second material comprises silicon.
 39. The laser opticallogic device of claim 38, wherein said pump comprises an optical pump.40. The laser optical logic device of claim 38, wherein said gain regionis substantially surrounded by said microstructure-doped mirror portionsin a selected plane.
 41. A laser optical logic device comprising: alaser comprising a light emitter comprising a first material andconfigured to emit light of a selected wavelength, said light emitterbeing physically embedded in an optically transmissive structure andhaving microstructure-doped mirror portions on at least four sides, saidmirror portions comprising a second material that is substantiallytransparent to the selected wavelength, said laser comprising saidoptically transmissive structure; a pump disposed with respect to saidlight emitter to pump said light emitter; at least one optical inputport to couple light into said laser; and at least one optical outputport to couple light out of said laser; wherein said laser has at leasta first state and a second state that affect a characteristic of lightcoupled out said at least one optical output port, light coupled intosaid at least one optical input port switching said laser from saidfirst state to said second state, and wherein said first materialcomprises PbS or HgTe and said second material comprises silicon. 42.The laser optical logic device of claim 41, wherein the pump comprisesan optical pump.
 43. The laser optical logic device of claim 41, whereinthe light emitter comprises a quantum dot.